1. Field of the Invention
This invention resides in the field of control materials for hematology instrumentation, with particular attention to red blood cell components of the control materials.
2. Description of the Prior Art
Hematology instruments for the analysis of blood components and chemistry have been used for many years, during which time the accuracy and sensitivity of these instruments have progressively advanced. The early forms of hematology instrumentation have thus been replaced by relatively complex machines that analyze the discrete components of blood based upon the intricate and subtle characteristics of each component.
The most recent iteration in automated hematology instrumentation has been the multi-part analysis of human white cells, in addition to the detection of red blood cells and platelets. White cell populations typically include lymphocytes, monocytes, neutrophils, basophiles, and eosinophils. The methods for blood cell analysis involve detection of the electrical and optical properties of each type of blood cell. A typical instrument will count and size red blood cells and platelets independently of the white cell component. To count white cells, it is necessary to destroy the red blood cells using a detergent such as a quaternary ammonium salt, leaving the white cells for counting and sizing.
The Beckman-Coulter™ five-part white cell analysis instrument uses several distinct technologies, variously based on electrical impedance, conductance (a DC mathematical manipulation that uses a low-voltage DC measurement), Rf (radio frequency) modulation, and laser technology which includes light scatter and light absorption. The Rf measurement is typically used with the DC low frequency measurement to create a parameter called opacity which is a calculation of Rf divided by DC. Instruments by other manufacturers, such as Abbott Diagnostics™, Bayer™, and TOA™ Medical Electronics, use a combination of electrical impedance, DC conductance and/or laser technology, Rf, depolarized 90° angle light scatter, and/or light absorption. Although the basic types of electronic technology may appear the same, each manufacturer has a unique implementation for the instrument hardware and software that is required to analyze blood cells. The individual implementations of this technology by the various manufacturers have resulted in a wide array of reagents and methodology for each specific instrument of each manufacturer, thereby increasing the complexity and expense of their use. No single reagent or methodology exists that can be used with a plurality of instruments.
To ensure the reliability and accuracy of hematology instruments, regulatory authorities require the use of blood controls to verify the integrity of the instruments. The optimal control contains particles that represent all of the cellular elements of fresh blood, together with a synthetic plasma, which is a liquid suspending medium artificially formulated to simulate human plasma. A synthetic plasma typically contains components that are the same as, or function in the same manner as, components of native plasma. These components include inorganic salts, organic and/or inorganic buffers, and a viscous material for maintaining a homeostasis similar to that maintained by plasma proteins. The manufacturer of a control provides all of the critical values such as cell count, cell size, and cell type. The control material should have sufficient shelf life to allow it to be used for days, weeks, or months, thereby ensuring the consistency of instrument performance over time.
The method for preparing a hematology control is dependent on the hardware and software design of the specific instrument in which the control is to be used, as well as the requirements for extended shelf life. Blood controls consist of an RBC component which is typically washed human red blood cells suspended in a synthetic plasma. The red blood cells are accompanied by one or more particles that will appear to the instrument as white blood cell sub-populations. While the white cell controls can be human white cells, are animal red cells that have been stabilized with a cross-linking agent to prevent them from being destroyed by a detergent are used as an alternative. Particles in blood control products that can serve as controls for human white cells, red blood cells, or platelets on a Coulter™-type instrument may not be effective for other instruments, such as those manufactured by Abbott Laboratories™, Bayer™, or TOA™ Medical Electronics. Moreover, because these particles are usually modified forms of various types of blood cells, they do not behave like living native fresh blood cells. For example, human white cells fixed with a cross-linking agent like glutaraldehyde may behave like a neutrophil on an Abbott™ instrument and like cellular debris on a Coulter™ instrument. Also, specially treated and cross-linked red blood cells from non-mammalian vertebrates may appear as mononuclear cells on one type of hematology instrument and as lymphocytes on another. The red blood cell component of a hematology control may serve well on a number of instruments for verifying numerical and chemical values such as count and hemoglobin content, as well as physical characteristics such as size and shape, and yet the values, particularly those of physical characteristics as mean cell volume (MCV), size distribution (RDW, i.e., red cell distribution width), and cell shape, can vary widely among different instruments. In addition, a red blood cell preparation may be read by one type of instrument as containing debris in the platelet and/or white cell counting regions and as containing no such debris by another type of instrument. For example, the red cell preparation in the Hematology (C) product manufactured by Bio-Rad Laboratories, Inc., has a high platelet background on the Bayer H1-E Hematology Instrument. On the Abbott CELL-DYN 4000 instrument, the same red blood cell preparation shows interference in the optical platelet and white cell regions. No platelet or white cell interference appears on the Abbott CELL-DYN 3000 series or 1000 series instruments. The red cell preparation used for the Bio-Rad Hematology (C) product shows no platelet or white cell interference on Coulter instruments as the Coulter Model MaxM but does show platelet and white cell interference on the Abbott CELL-DYN 4000 instrument.
The prior art contains reports of the addition of certain analytes to the suspending medium of a blood control to improve the performance of the red blood cell component in the control by modifying physical characteristics of the component and preventing the formation of particulate debris. Ryan et al., in U.S. Pat. No. 6,403,377 B1, teach the addition of lipoprotein to improve the size characteristics of white cell components and the addition of an anti-oxidant to prevent red blood cell lysis. The use of lipoprotein to increase the volume of the leukocyte components is likewise disclosed by Young, U.S. Published Patent Application No. US 2005/0221497 A1. In contrast to Ryan et al., the lipoprotein in Young serves to allow proper lysing of the red blood cells by a detergent used in the Coulter instrumentation. Young also describes the need for a non-ionic detergent in a blood control to further aid in red blood cell lysis without compromising the integrity of the white cell surrogates used in the blood control.
Fixation of red blood cells has been shown to be an effective method of providing non-lysable particles suitable for use as leukocyte analogs. Hunt, in U.S. Pat. No. 3,873,467, describes a fixation method for producing leukocyte analogs using human red blood cells. Ryan et al. above describe the stabilization of red blood cells using cross-linking agents. Cells that have been fixed by these methods are resistant to mechanical stress such as that induced by sonication. Young et al. above describe detailed fixation procedures for producing a number of different types of leukocyte analogs. Other fixation processes for leukocyte analogs are disclosed by Carver et al., in U.S. Pat. Nos. 6,146,901, 6,514,763B2, 4,704,364, and 5,380,664. All of the patents and published patent applications cited in this section and elsewhere throughout this specification are incorporated herein by reference.